Recently, intention to improve and preserve health with the aid of foods has increased and significance of vegetable foods has been increasingly recognized, resulting in expectation of a soymilk to serve as such a vegetable food. In response to the expectation, improved techniques for producing a soymilk have been developed independently of methods of producing a tofu (bean curd). As a result, soymilks in which bean smell, raw smell, bitter taste and astringent taste have been suppressed so as to be easy to drink have become commercially available. The wide variety of the improved techniques include removal of seed coats and hypocotyls, heating for inactivation of enzymes, treatment upon crushing and grinding, treatment upon separating tofu refuse, steps of sterilization and deodorization.
Such improved soymilks are remarkably easy to drink as compared to conventional soymilks. However, they still remain to be improved if they are used as materials for drinks or desserts although the bean smell, raw smell, bitter taste and astringent taste characteristic of soybeans have been improved to some extent.
In order to overcome the problems concerning the flavor of soymilks, they were conventionally seasoned with sweeteners, various flavors, fruit juices etc. for masking bean smell, raw smell, bitter taste and astringent taste characteristic of soybeans. However, such treatments are still insufficient. In addition, the flavors are unnatural. No method has been developed for producing a soymilk which can be utilized as a kneading material for confectionery or bakery and a filling material such as cream, as well as materials for fermentation foods, drinks, ice creams, desserts, aquatic or live-stock paste products, cooked daily dish and the like while retaining the natural flavor of soybeans
The present inventors directed their attention to the excellent flavor of a tofu prepared from a soymilk by a traditional method. Then, the present inventors began to examine a method of producing a liquid tofu with a tofu flavor, i.e., a soymilk which has low viscosity, does not re-coagulate, and can be utilized as a kneading material for confectionery or bakery and a filling material such as cream, as well as materials for fermentation foods, drinks, ice creams, desserts, aquatic or live-stock paste products, cooked daily dish and the like. In the course of the examination, it revealed that various methods for enriching soymilks with calcium have been examined, which provide similar effects, although the methods were developed for different purposes than those of the present inventors. Specifically, various methods have been proposed as follows for overcoming problems of increased viscosity due to aggregation of calcium with proteins in a soymilk or of coagulation into tofu-like state upon addition of the calcium into the soymilk.
For example, JP-A 52-90662 and JP-A 53-96356 disclose a method comprising adjusting pH by adding calcium hydroxide, a fat and an emulsifying agent to a soymilk. JP-A 53-183669 discloses a method comprising adding a chelating agent. JP-A 54-95771 discloses a method comprising adding casein and/or dephosphorylated .beta.-casein to an aqueous solution of soybean protein followed by addition of a calcium salt solution. JP-A 59-6839 discloses a method comprising partially hydrolyzing separated proteins, adding a fat and calcium glycerophosphate, and homogenizing the mixture. JP-A 59-173044 discloses a method comprising adding calcium lactate and sodium hydrogencarbonate in combination to a soymilk. JP-A 60-47636 discloses a method comprising incorporating a calcium compound into a soymilk in the presence of glycerol or propylene glycol. JP-A 61-25458 discloses a method comprising adding saccharide lime to a soymilk or a soybean protein drink and neutralizing the mixture with an organic acid. JP-A 61-249355 discloses a method comprising contacting a soymilk with a calcium-type strong acid cation-exchange membrane. JP-A 5-308900 discloses a method comprising adding calcium to a solution of separated soybean proteins and various soymilks, coagulating proteins, homogenizing the mixture, adding an acidulant, and homogenizing and heat-sterilizing the mixture.
However, none of the above-mentioned methods teaches a method comprising adding a coagulant for soybean proteins, then sterilizing the mixture with direct high-temperature flash heating using steam and homogenizing it.